Best practice in LUN design

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    The LUN design "question"

    How many LUN, how bigger (or smaller), on how many physical disks?

    You can find different post about this "problem"...


    There isn't a simple answer, cause it depends on:

    • Storage best practice

    • Storage type and disks type

    • RAID level and number of physical disks

    • VM number, size and type of I/O

    • Max VM and I/O per LUN

    • Max LUN size (less than 2 TB - 512B)


    Generally it's not a good idea to have very large LUNs: when you have a large number of VMs on a single VMFS based block device you will see a higher level of SCSI Reservation Conflicts which always results in performance degregation.

    This occurs because the clustered VMFS LUN uses a file lock control function from the hosts and the higher the VM count the more often they have to wait on each others update housekeeping I/O activity.


    See also:

    SAN Configuration Guide -

    SAN Conceptual and Design Basics -

    SAN System Design and Deployment Guide -



    LUN size

    Usually a value between 400-800GB could be reasonable.

    There is also a way to calculate the size, see on this site:

    Storage: How to size your LUNs? -


    Here are some good threads that talk about this....,289483,sid179_gci1350469,00.html

    LUN size

    Re: Disk files and LUN's

    Re: Sizing LUN for enough free space after VM

    San Sizing documentation request...

    Smaller LUNs or Bigger LUNs?

    Larger LUN = More Disks = More Performance

    Best Practice LUN Size

    Storage LUNs Size Sweet Spot



    LUN number

    Usually more that one, but not too much...

    It is also related by LUN size and how storage works (it works with RAID group or with a "global" RAID splitted on all disks)


    Here are some good threads that talk about this....

    Re: which is better, more or fewer disks for VM local storage??

    Re: Should we have one Large VMFS-3 volume or small Multiple volumes?

    Re: which is better, more or fewer disks for VM local storage??



    RAID level

    Re: How to configure the raid while installing the ESX Server

    ARTICLE: RAID 5/6 Scaling (Tom's HW)